Power output from PV cells varies according to their load current, the voltage at which they are operated, and stimulus or light level. Maximum Power Point (MPP) tracking techniques are intended to control operating voltages so that PV cells are operated at or near their maximum power points.
Some MPP tracking techniques, generally known as “perturb and observe” techniques, sample output power and change operating voltage depending on how the output power changes in successive sampling periods. However, some of these techniques do not differentiate between output power changes that are due to operating voltage changes and those that are due to changes in light level. Light level effects can result in incorrect adjustments to operating voltage, which increases convergence time and decreases effectiveness of the tracking algorithm.
Even in the absence of light level effects (i.e., constant irradiance), the pure “perturb and observe” algorithm will oscillate around the maximum power point with a given step, which would degrade the overall performance compared to the ideal maximum power point. Reducing the step to improve the static performance would degrade significantly the dynamic tracking capabilities of such an algorithm.